1. Field of the Invention
The invention relates generally to a field effect transistor (FET) and more specifically to a normally off Schottky barrier field effect transistors.
2. Description of the Prior Art
Field effect transistors, depending upon their structure, are either junction FETs or insulated gate FETs. The insulated gate FETs generally have a spaced drain and source regions formed in a substrate of opposite conductivity type. The source and drain are separated by a channel region upon which a gate is formed. The channel and the gate are separated by an insulator which may be a generic insulator or an oxide.
A common problem of insulated gate field effect transistors (IGFET) is the inversion or depletion of the channel in the substrate by interaction with the gate metal. One solution presented by the prior art is to use a semi-conductor gate instead of a metal gate in contact with the insulator over the channel.
In junction field effect transistors (JFET), the principles of the Schottky barrier have been incorporated. Schottky barrier sources and drains have been produced by forming metal electrodes directly on the ends of the channel regions. Similarly, modulation of the channel region has been effected by Schottky barrier gate electrodes formed directly on the channel region.
Though a majority of the prior art devices have been directed to normally on or depletion mode Schottky barrier FETs, there has been some fabrication of normally off or enhancement mode Schottky barrier FETs. The normally off Schottky barrier FETs of the prior art may only be forward biased only a few tenths of a volt to avoid drawing excess gate current. The limitation on the forward biased voltage of the prior art normally off Schottky barrier FETs limits the range of modulation.